FLAVIN ADENINE-DINUCLEOTIDE AND FLAVIN MONONUCLEOTIDE METABOLISM IN RAT-LIVER - THE OCCURRENCE OF FAD PYROPHOSPHATASE AND FMN PHOSPHOHYDROLASE IN ISOLATED-MITOCHONDRIA
M. Barile et al., FLAVIN ADENINE-DINUCLEOTIDE AND FLAVIN MONONUCLEOTIDE METABOLISM IN RAT-LIVER - THE OCCURRENCE OF FAD PYROPHOSPHATASE AND FMN PHOSPHOHYDROLASE IN ISOLATED-MITOCHONDRIA, European journal of biochemistry, 249(3), 1997, pp. 777-785
In order to gain some insight into mitochondrial flavin biochemistry,
rat liver mitochondria essentially free of lysosomal and microsomal co
ntamination were prepared and their capability to metabolise externall
y added and endogenous FAD and FMN tested both spectroscopically and v
ia HPLC. The existence of two novel mitochondrial enzymes, namely FAD
pyrophosphatase (EC 3.6.1.18) and FMN phosphohydrolase (EC 3.1.3.2), w
hich catalyse FAD-->FMN and FMN-->riboflavin conversion, respectively,
is shown. They differ from each other and from extramitochondrial enz
ymes, as judged by their pH profile and inhibitor sensitivity, and can
be separated in a partial FAD pyrophosphatase purification. Digitonin
titration and subfractionation experiments show that FAD pyrophosphat
ase is located in the outer mitochondrial membrane and FMN phosphohydr
olase in the intermembrane space. Since these enzymes can metabolise e
ndogenous FAD and FMN, which are made available by using both Triton X
-100 and the effector oxaloacetate, a proposal is made that FAD pyroph
osphatase and FMN phosphohydrolase play a major role in mitochondrial
flavoprotein turnover.